I wear a steel glans ring most days in order to help make my foreskin stay retracted, though I remove it at night. It is not tight enough to restrict blood flow - my glans has expanded, but that may just be the result of keeping it uncovered.
You need to choose a ring that fits snugly over your shaft when soft. The rim of the glans should keep it in place. It looks from your pic like you are circumcised, and have a prominent rim, so that should be no problem! You do need to squeeze the head through, as it is bigger than the ring - sometimes a little lube helps.
Hope this is some use!